Abstract
One side of potato tuber slices having different thickness was inoculated with such dense zoospore suspensions of an incompatible race of Phytophthora infestans as to infect almost all of the surface cells. The less the number of layers of underlying healthy cells, the more prolonged the time taken for the infected cells to die hypersensitively. Browning of the infected cells occurred more rapidly in thick slices than in thin slices. These results suggested that healthy cells underlying the infected cells play an important role in the hypersensitive death of the infected cells and also supply substances necessary to localize the infection.